A composite material which is reinforced by carbon fibers has been widely used as a structural material of an airplane or a vehicle, or as materials in the general or sport industry such as a tennis racket, a golf shaft, or a fishing rod due to its high specific strength and high specific elasticity. Examples of the form of carbon fibers used for these materials include woven fabric which is formed using continuous fibers, an UD sheet in which fibers are unidirectionally arranged, a random sheet which is formed using cut fibers (discontinuous fibers), and non-woven fabric.
Recently, a composite material in which a thermoplastic resin is used as a matrix instead of a thermosetting resin of the related art has attracted attention. For example, a molding method is developed including: heating a carbon-fiber-reinforced resin composite material impregnated with carbon fibers and a thermoplastic resin to a softening point of the thermoplastic resin or higher; putting the resin material into a mold whose temperature is adjusted to a melting point or lower or a glass transition temperature or lower; and shaping the resin material by mold clamping. A carbon-fiber-reinforced resin composite material having a small unevenness in areal weight is also developed (Patent Documents 1 and 2).
Patent Document 1 describes a method of obtaining a shaped product including: impregnating a thermoplastic resin with continuous carbon fibers, which are unidirectionally arranged, to obtain a thermoplastic resin prepreg; cutting the thermoplastic resin prepreg into short pieces; and press-molding the short pieces. According to Patent Document 1, the unevenness in areal weight can be suppressed by using carbon fibers having a specific average single fiber fineness and a specific roundness.
Patent Document 2 describes a method of obtaining a papermaking base material having an excellent dispersed state of reinforcing fibers and a small unevenness in areal weight at a low cost. According to Patent Document 2, by precisely controlling the addition of carbon fibers during papermaking using a specific method, the papermaking base material having an excellent dispersed state of reinforcing fibers and a small unevenness in areal weight can be prepared.